低温烧结AlN陶瓷的微结构和热导率

采用CaF2，Y2O3和Li2CO3做添加剂，在低温下制备了高热导率的AlN陶瓷，通过SEM，TEM和XRD研究了AlN陶瓷在烧结过程中微结构及晶格常数的变化及其对热导率的影响。研究发现，当使用CaF2-Y2O3做添加剂时，液相对晶粒浸润性较差。不利于AlN晶格的纯化。而添加Li2O-CaF2-Y2O3的AlN陶瓷在烧结温度之前已经完成了液相的重新分布，液相与AlN晶粒之间有较好的浸润性，这促进了AlN陶瓷的致密化和AlN晶格的纯化，有利于获得较高的热导率。     

Li2O对低温烧结AlN陶瓷热导率的影响

使用CaF2,Y2O3和Li2Co3做添加剂，在1650℃的低温下制备出热导率高于170W/m.K的AlN陶瓷，通过使用SEM，TEM和XRD研究了AlN陶瓷在烧结过程中微结构与晶格参数的变化，并讨论了其对热导率的影响，研究发现，当使用CaF2-Y2O3做添加剂时，液相对晶粒浸润性较差，不利于AlN晶格的纯化，AlN热导率的增加主要来自于致密度的提高，而Li2O的加入则改善了液相与AlN晶粒的浸润性，从而促进了AlN晶格的纯化，有利于获得较高的热导率。     

Li2O对低温烧结AlN陶瓷热导率的影响

使用CaF2,Y2O3和Li2CO3做添加剂,在1650℃的低温下制备出热导率高于170W/m@K的AlN陶瓷,通过使用SEM,TEM和XRD研究了AlN陶瓷在烧结过程中微结构与晶格参数的变化,并讨论了其对热导率的影响.研究发现,当使用CaF2-Y2O3做添加剂时,液相对晶粒浸润性较差,不利于AlN晶格的纯化,AlN热导率的增加主要来自于致密度的提高.而Li2O的加入则改善了液相与AlN晶粒的浸润性,从而促进了AlN晶格的纯化,有利于获得较高的热导率.     

高热导率氮化铝陶瓷的研究进展

简要介绍了AlN陶瓷的导热机理和影响因素,主要报道制备氮化铝陶瓷过程中提高热导率的措施。阐述了添加剂的作用机理,以及不同添加剂对AlN陶瓷的致密化和烧结温度的影响,概括了目前AlN陶瓷的成型和烧结方法,分析了后续热处理对AlN陶瓷显微结构和热导率的影响。     

复合助剂CaF2-Y2O3对AlN-BN复合陶瓷显微结构和热导性能的影响

用热压法制备了AlN-BN复合陶瓷材料,添加CaF2和Y2Os为烧结助剂,研究了烧结助剂的种类、含量以及不同保温时间对复合材料的物相组成、显微结构和热导率的影响.添加复合助剂(1～3)wt%Y2O3-3wt?F2的试样在保温过程中晶界相挥发明显,净化了复合材料的晶界,减少了复合材料中AlN晶格缺陷,获得了纯净的AlN-BN复合陶瓷.与单独添加CaF2助剂的试样相比,添加复合助剂的试样的介电性能没有明显下降,随复合助剂(1～3)wt%Y2O3-3wt?F2中Y2O3含量的增加,AlN-BN复合陶瓷的热导率显著提高.添加复合助剂3wt%Y2Os-3wt?F2的试样在1850℃下保温3h获得的热导率为132.7W·m-1·K-1.     

热压烧结工艺对AlN陶瓷显微结构及性能的影响

以直接氮化法制备的AlN粉体为原材料,添加质量分数为5％ 的Y2O3做烧结助剂,采用热压烧结工艺制备AlN陶瓷.研究烧结温度和压力对AlN陶瓷显微结构、相对密度和热导率的影响.结果表明:随着烧结温度的升高,AlN陶瓷的晶粒长大,第二相逐渐增多,热导率和相对密度均为先增大后减小;随着压力的增大,AlN陶瓷的晶粒逐渐细小,气孔率减少,热导率和相对密度都显著增大.确定AlN陶瓷的最优烧结条件如下:温度为1800℃,压力为50 MPa.     

烧结助剂及Mo含量对AlN-Mo复合陶瓷热导率的影响

以CaF2、CaCO3为烧结助剂,采用热压烧结法制备了AlN-Mo复合材料。利用XRD和SEM分析了AlN-Mo复合陶瓷的相组成及其微观形貌,并讨论了烧结助剂和Mo含量对该材料热导率的影响。结果表明,CaF2和CaCO3烧结助剂的添加量在1%～3%(质量分数)范围内,AlN-Mo复合材料的热导率随着CaF2含量的增加而升高,随着CaCO3含量的增加先升高后降低。在烧结助剂的种类和含量一定时,含20%(体积分数)Mo的AlN-Mo复合陶瓷的热导率高于含18%(体积分数)Mo的AlN-Mo复合陶瓷的热导率。     

AlN陶瓷热导率影响因素的研究

基于AlN陶瓷的导热机理，从显微结构、材料组成、工艺因素三方面来对AlN热导率的影响进行了探讨。AlN高热导率取决于AlN晶间良好接触、第二相含量少呈孤岛状分布以及低气孔率的显微结构，而材料组成、制备工艺的优化是为了具有良好显微结构的AlN陶瓷得以实现和改善。     

热压烧结AlN(Y_2O_3)陶瓷热导率的温度关系

采用热压烧结技术,以Y2O3为烧结助剂制备AlN陶瓷。闪光法测试AlN陶瓷在室温~200℃的温度关系。结果表明,AlN陶瓷热导率随温度升高而降低;气孔对AlN陶瓷热导率随温度变化的速率有抑制作用,气孔率越小(致密度越高),热导率对温度变化越敏感;AlN陶瓷钇铝酸盐晶界相含量对热导率随温度变化的速率有促进作用,钇铝酸盐含量越高,热导率对温度变化越敏感。     

Y2O3和纳米AlN协同作用对氮化铝陶瓷烧结性能及热传导的影响

在微米氮化铝粉体中添加含量为4%的Y2O3和不同含量的纳米AlN粉体制备氮化铝陶瓷,研究了Y2O3和纳米AlN协同作用对微米氮化铝陶瓷烧结性能和热传导性能的影响。结果表明,Y2O3优先与纳米AlN粉体表面的Al2O3反应生成活性较高的第二相Al5Y3O12,相比于Y2O3与微米AlN粉体表面Al2O3反应生成的Al5Y3O12,具有更低的熔化温度及更好的流动性;同时,纳米AlN粉体的高比表面能也促进氮化铝陶瓷的致密化进程。二者的协同作用有效地促进氮化铝陶瓷的致密烧结,改善第二相的微观分布,从而能在较低的烧结温度下获得具有较高热导率的氮化铝陶瓷。当Y2O3和纳米AlN粉体的添加量(质量分数)分别为4%和1.5%时,在1800℃烧结得到的氮化铝陶瓷密度为3.26 g·cm-3,第二相以连续相的形式分布于氮化铝晶界处,热导率为151.75 W/(m.K)。     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.     

Early ironwork in Biscay: Survey,excavation, experimentation and materials characterization. An integral study of the mountainside ironworks (ferrerías de monte or “haizeolak”)

ABSTRACT

The production of iron in Biscay (Basque Country, Spain) has been a hallmark of this territory of the North of the Iberian Peninsula throughout its history. The Archaeology team of the Basque Country Mining Museum has spent 13 years, so far, studying the origins of this activity through the evidences left at the old pre-hydraulic iron production workshops known as mountainside ironworks (ferrerías de monte) or haizeolak. It has catalogued 170 archaeometallurgical sites of this type in Biscay, and the archeological excavation of some of them has led to the knowledge of the different stages of the production process that took place in these workshops. The team has also experimentally reproduced the work carried out in a mountainside ironworks from the High Middle Ages, and it has currently started the characterization process of this type of activity through the study of the collected materials.     

Mechanism Study on the Wear of CrAlTiN Coated High-Speed Steel Twist Drills Under Dry Cutting Conditions

As demands about environment protection are growing up, dry cutting technology is getting more and more concerns from all over the world. Main works performed here are study on dry cutting performances and wear mechanisms of M2high-speed steel (HSS) twist drills with CrAlTiN multicomponent coatings, which was deposited using magnetron sputter ion plating system, in drilling 45 and 30CrMnSiA steel, and their comparisons to those in drilling the same steel but using monolayer CrN and commercial TiN coated drills. Drilling performances of drills are evaluated mainly through the measurements of width on outer corner flank land and the cutting forces. Results show that performances of CrAlTiN coated drills are better than those of monolayer CrN and TiN coated drills. In drilling 45 and 30CrMnSiA steel, the average tool life of the CrAlTiN coated drills are 17.2 and 11.8 times higher than those of the uncoated drills. Observing wear of the drill with scanning electronic microscope, results show that there is no crack or spallation of the CrAlTiN coatings in wear zones. Main mechanism of the wear here is adhesion.     

Study on Bond Ability of Arc-Spraying Coatings with Different Surface Pretreatment on Cast-Iron

Arc spraying coatings are widely used in various applications, but uncommon in cast iron substrate. Different surface pretreatment technology is tested on substrates of gray cast iron. Surface roughness and residual stress were measured by TR200 and X-ray diffraction analyzer. Influence of different surface pretreatment methods ( dry blasting and fusebond) on roughness and residual stress was analyzed. The arc-sprayed coatings of wire 3Cr13 (φ2mm) on gray cast iron substrate is studied. The microstructure and interface of bonding layer were observed by SEM. The bond strength was taken by tensile test. Results show that bond strength with grit blasting is higher than fuse-bond; it is feasible to make wire 3Cr13 coating with arc spraying on cast iron substrate roughened by grit blasting.     

Structural Characteristics of TiO2 Ceramic Coating by Micro-Plasma Oxidation

TiO2 ceramic coatings with thickness of 20 μm were formed on the surface of pure titanium by micro-plasma oxidation. Their micro-structures were investigated by by using X-ray diffraction and their surface images were detected by using scan electronic microscope. There were three kinds of TiO2 coatings, pure anatase type TiO2 phase, mixed phases consisted of rutile type TiO2 phase and anatase type TiO2 phase, pure rutile type TiO2 phase. The coating surface with the pure anatase type TiO2 phase is rough, while the coating surface with the pure rutile type TiO2phase is smooth. The upper coating surface with the mixed type TiO2 phases is anatase type TiO2 structure and the subsurface of the TiO2 coating is rutile type TiO2structure.     

Evaluation of fatigue life of steel using steel grain size

The insightful discussion of the relationship between the construction of metallographic and fatigue life and proposition of mathematical relationships describing this relationship was conducted in the paper. This paper presents a method for estimating the fatigue life, based on the construction of the microstructural material taking into account the grain size and the participation of ferrite and pearlite phase.